Abstract
The use of air photographs in interpreting some geological features of the Canadian Shield is illustrated and the method applied to several large areas. It is shown that many large faults can be distinguished. With the aid of existing field data and physical theory, an attempt is made to classify these structure's and to show the direction of the major orogenic forces which produced them. The faults have been divided into groups which it is suggested are connected with the folded roots of several former mountain ranges. The arrangement of these and later ranges outside the Shield suggests that the North American continent has grown by the accretion of successive systems of mountain arranged tangentially along the former margins of the continent.

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